This invention relates to grinding machines and more particularly to high-precision grinders using CNC controls.
Definitions: xe2x80x9cCNCxe2x80x9d refers to computer numerical control systems as employed for operation of machine tools.
xe2x80x9cChuckerxe2x80x9d refers to a workhead for a grinding or turning machine having a clamping device or chuck capable of holding only a part short enough not to require a tailstock at the opposite end of the part during grinding or turning. No part support other than the chuck is provided at the driven end of the part.
Grinding machines using a single workhead and a CNC control system have been employed previously for high-precision applications. Prior grinders of this type have generally coupled a CNC control system to a grinding wheel spindle for movement along an in-feed axis, which brings the wheel into contact with a supported workpiece being held in position on a single workhead by a chuck or other clamping device. The workhead in this approach is not fed into the wheel for grinding, but is held in place once adjusted.
It would be advantageous to provide improved CNC chucker grinders capable of providing increased production rates without sacrificing any of the high degree of precision obtained.
The present invention is directed to a grinding machine comprising a grinding wheel and a pair of workheads mounted on supporting structure enabling independent movement of the workheads toward and away from the grinding wheel, with operation of the workheads and chucks attached thereto being carried out under separate and independent CNC controls.
Supporting structure for the workheads includes a horizontally extending base having a generally flat bed surface carrying laterally extending linear rails or V and flat linear motion guides adapted for receiving mating elements placed underneath a pair of aligned workslides. Movement of the workslides in a lateral direction, generally parallel to the grinding wheel spindle, may be carried out by linear ball screws driven by servo motors. The ball screws typically are rotatably mounted in bearing blocks or housing and are connected to ball nuts which are fixedly attached to the workslides.
Each of the workslides carries a cross slide and connecting elements necessary for support and movement of an upper platform of the cross slide in a direction perpendicular to the wheel spindle. The platform rests on a lower block portion of the workslide, with linear rails attached to the lower portion and mating elements provided underneath the upper platform. Movement of the cross slide is enabled by use of a ball screw, bearing blocks or housings and a driving servo motor in a manner. similar to those used for work slide movement.
A spindle case aligned for driving a workhead chuck is provided of the upper platform of each cross slide. A spindle carried in the case extends from the innermost side of the. case and has a spindle nose which serves as a plate for attachment of a rotatable chuck. The chuck is driven by a servo motor placed alongside and propelling a belt engaged with pulleys on the motor and spindle.
The machine may thus provide for controlled linear movement of both workheads and a wheelhead along five or more linear axes and for controlled rotary movement of each of two chucks around rotary axes. Each of the movements involved is controlled by the CNC System of the machine. In order to obtain high precision between workpieces being simultaneously ground-while supported on dual workheads, each of the workheads is controlled independent. of the other, but in coordination with control of the grinding wheel.
The CNC control system may make use of computer software programmed to include parameters such as extent and timing of movements, grinding speeds, starting and final dimensions of workpieces and the like. Additional data entries and modifications may be inserted by a keyboard operater using conventional techniques. Information derived from in-process gauges may also be fed into the control system to provide precision timing of grinding shutoffs. By using independent CNC controls for the two workheads, separate workpieces may be ground to meet the same or different requirements. Grinding of one workpiece may be completed and terminated by retracting its workhead while the other is still being ground.
Grinding machines of this invention provide a high degree of precision such as 20 millionths of an inch. This result is enabled by various factors, including use of servo motors having a resolver or encoder capable of providing a high number of incremental counts per revolution such as 4,000,000. This level of precision would not be available if a single CNC control were used in propelling a grinding wheel against a pair of separately supported workpieces.
An increased production rate, twice the rate for single workhead machines once set-up is performed, may be obtained by this invention without any compromise of precision.
It is, therefore, an object of this invention to provide a high-precision grinding machine capable of operating at an increased production rate.
Another object is to provide a grinding machine wherein a pair of independently controlled workpieces may be ground simultaneously on a single grinding wheel.
Other objects and advantages of the invention will be apparent from the following detailed description and claims appended hereto.